The invention relates to data storage disk drives, and particularly to the control of the magnitude of vibrations generated and transmitted by the components of a disk drive at rocking mode and diaphragm mode resonant frequencies during operation of the disk drive.
Disk drives are used in computer applications for the high volume storage of data. Modern hard disk drives contain a disk assembly mounted within a disk enclosure or housing. The assembly includes a special head arrangement for transferring data to and from circular tracks disposed concentrically on multiple disk surfaces while the disks are rotated on a spindle mechanism at a predetermined speed. The disk enclosure containing the disks and the actuator with head-arm assemblies is also known as the head-disk assembly (HDA).
In a typical hard disk drive spindle arrangement, the disks are clamped to a bearing-mounted spindle hub which can rotate about an inner stationary spindle shaft. The disk drive spindle arrangement with mounted disks is referred to as the spindle-disk assembly (SDA). A motor mounted within the hub rotates the hub and disks. The motor is typically of the brushless DC type, consisting of a stator fixedly attached to the spindle shaft and a permanent magnet ring fixedly attached to the hub so that energization of the stator causes the hub, and thus the disks, to rotate.
The SDA of a disk drive has essentially three major modes of vibration: disk and hub vibrations in a radial direction relative to the spindle shaft; disk and hub vibrations in an axial direction relative to the spindle shaft; and a rocking (or wobbling) displacement of the disk and hub relative to the spindle shaft. The SDA (specifically the disks and the hub) exhibits the aforementioned modes of vibration as a result of the following types of excitations: 1) spindle generated vibrations such as "ball bearing ball pass" and "ball spin" during normal operation, 2) environmental vibrations and shocks, and 3) vertical diaphragm mode vibrations of the HDA that are transferred to the SDA. Diaphragm mode vibrations are vertical drum-like deformations of both the top cover and the bottom base plate of a disk enclosure/HDA.
Prior art disk drives have precision spindle assemblies with rigid shafts mounted directly to very rigid housings. These disk drives, because of their mechanical structure, offer minimal damping to attenuate the effects of spindle rocking mode and vertical diaphragm mode resonances caused by environmental shocks and vibrations, and spindle generated excitations during normal operation. Some of the vibrational energy transmitted to the SDA coincides with its inherent resonant frequencies, causing servo system errors and track misregistration thereby resulting in decreased drive performance. Further, due to the smaller height and closer spacing between spindle bearings, low profile disk drives have lower resonance frequencies for the SDA rocking modes thereby experiencing performance problems at lower frequencies of excitations.
The mechanical structure of an SDA has a significant effect on the amplitude of vibrations experienced by it at spindle rocking mode and vertical diaphragm mode resonant frequencies. Undamped, rigid mechanical structures have lower resonant frequencies than damped structures having the same effective stiffness. They also exhibit vibrations of higher amplitude at resonant frequencies. Therefore, an undamped and rigid SDA attains its structural resonance frequencies at lower levels of excitation and also experiences large vibrations at its resonance frequencies. These vibrations cause the servo system to fail resulting in both write-to-write and write-to-read track misregistration. Therefore, the mechanical structure of an SDA has a significant effect upon the capability of a storage system to support high track and bit densities and upon its performance characteristics.
Therefore, there is a need for dynamically stable disk drives having additional internal damping to reduce the amplitude of vibrations experienced by the SDA at spindle rocking mode and vertical diaphragm mode resonant frequencies caused by environmental shocks and vibrations, and spindle generated excitations during normal operation.
Further, low acoustic noise is an increasingly important performance advantage in the hard disk drive market; particularly, for example, for hard drives designed to operate in personal computers for use in relatively quiet environments. It has been found that a major source of acoustic noise is the excitation of SDA during normal operation.
Therefore, there is also a need for quieter hard disk drives having damping for improved acoustic performance.